Utilizing Eco-Friendly Zinc Oxide Nanoparticles for Enhancing Growth and Controlling Downy Mildew in Pearl Millet -

Utilizing Eco-Friendly Zinc Oxide Nanoparticles for Enhancing Growth and Controlling Downy Mildew in Pearl Millet

Introduction: The research paper explores the innovative use of biofabricated zinc oxide nanoparticles as an environmentally friendly solution for promoting growth and effectively managing downy mildew in pearl millet. By synthesizing these nanoparticles using a saponin-rich fraction from the aqueous extract of Eclipta alba, the study aims to investigate their impact on seed germination, plant vigor, and disease resistance. Through laboratory and greenhouse experiments, the efficacy of the nanoparticles in enhancing pearl millet growth and combating downy mildew is evaluated. The findings shed light on the potential of these nanoparticles to serve as a sustainable alternative for agricultural practices, offering promising results for both plant development and disease control.

Material and Methods:

Synthesis of Zinc Oxide Nanoparticles: The zinc oxide nanoparticles were synthesized using a saponin-rich fraction from the aqueous extract of Eclipta alba. The synthesis was carried out by mixing 0.1 M zinc nitrate and 0.1 M sodium hydroxide solutions with the saponin-rich fraction. The mixture was stirred for 24 hours at room temperature, followed by centrifugation and washing with distilled water. The nanoparticles were then dried and characterized using various techniques.

Characterization of Nanoparticles: The synthesized nanoparticles were characterized using UV spectroscopy, FTIR, SEM, XRD, DLS, and EDAX analysis. The UV spectroscopy was used to determine the absorbance of the nanoparticles, while FTIR was used to identify the functional groups present in the nanoparticles. SEM and XRD were used to determine the morphology and crystal structure of the nanoparticles, respectively. DLS was used to determine the size distribution of the nanoparticles, and EDAX was used to determine the elemental composition of the nanoparticles.

Plant Material and Growth Conditions: Pearl millet (cv. 7042S) seeds were obtained from a local seed supplier. The seeds were surface sterilized with 70% ethanol and 0.1% mercuric chloride solution and washed with distilled water. The seeds were then soaked in distilled water or nanoparticle suspension for 24 hours before sowing. The seeds were sown in earthen pots filled with autoclaved soil and sand in a 2:1 ratio. The plants were grown in a greenhouse under controlled conditions of temperature (25 ± 2°C) and humidity (60 ± 5%).

Downy Mildew Inoculation: Three-day-old seedlings were challenge inoculated with zoospore suspension of Sclerospora graminicola in the early morning for three consecutive days. In another set, foliar spray with 150 ppm of ZnO nanoparticle was given one day before challenge inoculation. The experiment was done in triplicates, each pot contained 10 seedlings each and repeated thrice. The treatments were arranged in randomized block design.

Analysis of Plant Growth and Disease Resistance: The plants were observed for typical downy mildew symptoms such as stunted growth, chlorosis, and sporulation on the abaxial leaf surface. The percentage disease protection was calculated in comparison to distilled water control. The plant height, fresh and dry weight of seedlings were measured. The zinc content in nanoparticle treated seedlings was determined using inductively coupled plasma mass spectrometry analysis. The defense enzymes such as peroxidase, phenylalanine ammonia-lyase, lipoxygenase, and polyphenol oxidase were analyzed. Semi-quantitative RT-PCR analysis was performed to determine the expression of defense enzyme genes.

Results:

Seed Treatment with Zinc Oxide Nanoparticles: Seed treatment with synthesized zinc oxide nanoparticles significantly enhanced pearl millet seed germination, vigor, plant height, and fresh and dry weight of seedlings. The zinc content in nanoparticle-treated seedlings was higher compared to control seedlings, indicating successful uptake of zinc from the nanoparticles.

Downy Mildew Management: Foliar spray with zinc oxide nanoparticles one day before challenge inoculation resulted in a 35% reduction in downy mildew incidence compared to the untreated control. Nanoparticle-treated seedlings exhibited high lignification and callose deposition upon downy mildew infection, indicating enhanced defense responses.

Defense Enzyme Activities: Analysis of defense enzymes showed that nanoparticle treatment significantly enhanced the activities of peroxidase, phenylalanine ammonia-lyase, lipoxygenase, and polyphenol oxidase compared to the untreated control. Semi-quantitative RT-PCR analysis revealed overexpression of defense enzyme genes in nanoparticle-treated seedlings, indicating the induction of defense mechanisms.

Discussion:

Growth Promotion: The synthesized zinc oxide nanoparticles effectively promoted seed germination, plant growth, and vigor in pearl millet, highlighting their potential as a growth-promoting agent in agriculture.

Downy Mildew Management: The nanoparticles demonstrated efficacy in managing downy mildew by reducing disease incidence and inducing defense responses in pearl millet plants.

Defense Mechanisms: The nanoparticles triggered the activation of defense enzymes and defense gene expression, leading to enhanced resistance against downy mildew infection.

Conclusion:-

In conclusion, the study demonstrates the potential of biofabricated zinc oxide nanoparticles as an eco-friendly alternative for growth promotion and management of downy mildew in pearl millet. The nanoparticles effectively promoted seed germination, plant growth, and vigor, while also reducing disease incidence and inducing defense responses in pearl millet plants. The study highlights the promising potential of these nanoparticles as a sustainable solution for agricultural practices, offering a non-toxic and environmentally friendly approach to growth promotion and disease management.

Reference:-

NANDHINI, M., RAJINI, S.B., UDAYASHANKAR, A.C., NIRANJANA, S.R., LUND, O.S., SHETTY, H.S. AND PRAKASH, H.S., 2019. Biofabricated zinc oxide nanoparticles as an eco-friendly alternative for growth promotion and management of downy mildew of pearl millet. Crop Protection, 121, pp.103-112.